1. Field of the Invention
The present invention relates to a fulcrum member and, particularly, to an opposed type fulcrum member used in a lever detector and the like.
2. Description of the Related Art
In a pinching type lever detector that measures the inside diameter and outside diameter of a work, two finger arms to each of the leading ends of which contact pieces are attached are supported in such a manner as to permit seesaw motions around an opposed type fulcrum member and the amount of movement of each of the finger arms when the two contact pieces are caused to abut against the work is detected by the detector.
As a fulcrum member, a cross-shaped spring fulcrum as shown in FIG. 6A, an L-shaped spring fulcrum as shown in FIG. 6B, an elastic fulcrum as shown in FIG. 6C, a bearing not illustrated, etc. are used. A cross-shaped spring fulcrum is generally constructed by disposing two plate springs as shown in the left side part of FIG. 6A in a cross manner. In this type, however, assembling requires time and variations occur in the spring characteristics due to assembling errors. There is also a type in which as shown in the right side part of FIG. 6A, a cross-shaped spring is integrally formed by being cut from a wire. This type, however, had the problems that the manufacturing cost is high and that durability decreases due to microcracks in worked surfaces.
An L-shaped fulcrum is inexpensive and this is a fulcrum that has generally found wide use. However, this type has the disadvantage that the center of the fulcrum moves as a result of circling motions, and is not suitable for a high-accuracy fulcrum member. Although there is no limit to circulating angles, a bearing fulcrum requires periodical replacements because accuracy decreases due to wear.
An elastic fulcrum is suitable for a narrow measuring range because of high accuracy although circulating angles are small because of the utilization of elastic deformation.
An elastic fulcrum member 110 as shown in FIG. 5 is used in a pinching type lever detector that measures the inside diameter of a work. In this elastic fulcrum, as shown in FIG. 5, a cylindrical main body 111 is formed as a hollow body and a large opening 111B is formed on both sides except for a cylindrical base part 111A, whereby the whole main body 111 is formed to be roughly U-shape and a thin-walled part 111C is formed in two places near the cylindrical base part 111A, the thin-walled parts each serving as an elastic fulcrum.
In the pinching type lever detector 120, a coil spring 124 provided in the main body 111 urges the U-shaped main body in outward directions and the amount of displacement of contact pieces 121 attached to the leading ends of the main body is detected as the displacement of a coil 122 and a core 123 of a differential transformer. An inside diameter measuring device similar to this pinching type lever detector 120 is described in the Japanese Patent Application Laid-open No. 57-23806, for example.
There has been proposed a friction addition device that is based on the utilization of this elastic deformation and uses a lever member in which a thin-walled part is provided as a fulcrum (refer to the Japanese Patent Application Laid-open No. 11-311269, for example).